Which statement correctly differentiates a phased array transducer from a linear array?

• A. Linear array steers electronically with a small footprint; Phased array uses a fixed rectangular aperture.
• B. Phased array steers electronically with a small footprint; Linear array uses a fixed rectangular aperture.
• C. Phased array uses a curved aperture; Linear array has a fixed rectangular aperture.
• D. Phased array steers and focuses electronically with a small footprint; Linear array uses a rectangular fixed aperture.

Answer: (D)

The key idea is how the beam is formed and steered. A phased array uses many small elements with precise timing delays across them, so you can steer the beam and focus at different depths purely by adjusting these delays. That electronic control lets you aim the ultrasound in different directions without moving the probe, and you can dynamically focus as you scan. All of this happens within a compact, multi-element footprint because you’re packing a lot of tiny elements into a small area.

A linear array, by contrast, has a fixed rectangular aperture—the physical arrangement and size of the active elements don’t change during operation. Beam shape and direction can be manipulated with delays, but the aperture itself isn’t dynamically altered, and the geometry is typically a flat, rectangular surface. So the statement aligned with the fundamental difference is that a phased array steers and focuses electronically while maintaining a small footprint, whereas the linear array uses a fixed rectangular aperture.